1. Field of the Invention
The present invention relates to novel aqueous silicone dispersions based on an aminosilane and/or amidosilane, and, more especially, to such novel dispersions that are crosslinkable into elastomeric state upon removal of water therefrom.
2. Description of the Prior Art
U.S. Pat. No. 2,891,920 describes a process for emulsion polymerization of polydiorganosiloxane using an acidic or basic catalyst in the presence of anionic, cationic or nonionic surfactants. This '920 patent suggests that the emulsions obtained are stable on storage and are useful, after addition of fillers, for formulating paints which provide a continuous coating on removal of water therefrom.
U.S. Pat. No. 3,294,725 describes in particular, the use of dodecylbenzenesulfonic acid for the emulsion polymerization of polydiorganosiloxanes. This '725 patent offers that, to produce stable emulsions, it is desirable to adjust the pH of such emulsions to a value of approximately 7. It also relates that an elastomer coating may be produced from these neutralized emulsions to which colloidal silica and a polyalkoxysilane have been added.
The description of U.S. Pat. No. 3,360,491 is similar to that of U.S. Pat. No. 3,294,725, except that the dodecylbenzenesulfonic acid is replaced by lauryl hydrogen sulfate.
U.S. Pat. No. 3,697,469 describes a special process for emulsion polymerization of polydiorganosiloxanes, and notes the possibility of adding colloidal silica and a tin salt to the emulsion for the purpose of producing an elastomer coating upon evaporation of water therefrom.
French Patent FR-A-2,110,358 describes a silicone emulsion having a pH of from 6.5 to 9, which crosslinks into an electrically conducting elastomer after evaporation of water, on incorporation of carbon black therein. The emulsion additionally contains a tin salt and a polyalkoxysilane, is not stable on storage, and must be stored in two separate packs (two-component emulsion).
U.S. Pat. Nos. 4,221,688 and 4,244,849 and French Patent FR-A-2,463,163 describe storage-stable silicone emulsions which contain:
(i) an anionically stabilized emulsion of an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane polymer; PA0 (ii) a siliceous filler; PA0 (iii) a tin salt; and PA0 (iv) optionally, a non-reinforcing filler. PA0 (A) 100 parts by weight of an oil-in-water emulsion of an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane, stabilized with at least one anionic or nonionic surfactant or mixture thereof; PA0 (B) 0.1 to 20 parts by weight of a silane of the formula: ##STR1## in which X is a hydrolyzable group selected from an amino and an amido radical; R.sub.1 is a monovalent C.sub.1 -C.sub.13 hydrocarbon radical; R.sub.2 is a C.sub.1 -C.sub.8 aliphatic organic radical selected from among alkyl radicals, alkyl ether radicals, alkyl ester radicals and cyanoalkyl radicals or a C.sub.7 -C.sub.13 aralkyl radical; a is an integer equal to 2, 3 or 4; b is an integer equal to 0 or 1; and a+b is equal to 2, 3 or 4; PA0 (C) 0 to 3 parts by weight of a catalytic metal curing compound; PA0 (D) 0 to 250 parts by weight of a non-siliceous inorganic filler, said dispersion having a pH above 7, and preferably ranging from 8 to 13, and a dry solids content of at least 40%.
The siliceous filler can be a colloidal silica (U.S. Pat. No. 4,221,688), sodium silicate (U.S. Pat. No. 4,244,849) or an amorphous powdered silica (FR-A-2,463,163).
With respect to the known aqueous emulsions (dispersions) of the prior art, these three patents describe that, on the one hand, to obtain a one-component emulsion stable on storage, the emulsion must be stored at an alkaline pH above 8.5 or 9, and preferably above 10, and, on the other hand, that a tin salt should be incorporated in the emulsion in order to shorten to a few days the stage of maturation of the emulsion necessary for producing a dispersion capable of crosslinking.
U.S. Pat. No. 3,355,406 describes a silicone latex including an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane, preferably prepared by emulsion polymerization, and a silsesquioxane resin comprising RSiO.sub.1.5 units (R=hydrocarbon residue). The latex can contain, in addition, a metal curing catalyst and an alkyltrialkoxysilane.
In U.S. Pat. No. 4,554,187, the silicone resin combined with the .alpha.,.omega.-(dihydroxy)polydiorganosiloxane is a low molecular weight reactive resin having alkoxy or acyloxy groups.
In Patent Application EP-A-366,729, the silicone resin combined with the .alpha.,.omega.-(dihydroxy)polydiorganosiloxane and the curing catalyst is a siliconate.
A silicone resin containing up to 10% by weight of hydroxyl groups may be combined with this siliconate.
U.S. Pat. No. 4,618,642 describes an aqueous silicone dispersion containing a non-siliceous filler and an alkoxysilane or a ketiminoxysilane. According to U.S. Pat. No. 4,608,412, an alkyl orthosilicate is also useful. The aqueous dispersions obtained possess, however, insufficient storage stability.
The use of an alkoxysilane combined with a siliceous filler is, moreover, described in U.S. Pat. No. 4,618,645.
Aminosilanes and amidosilanes are known compounds, the combination of which, protected from atmospheric moisture, with an .alpha.,.omega.-(dihydroxy)diorganopolysiloxane and a curing catalyst, provides a one-component composition stable on storage in the absence of water and crosslinking into an elastomer in the presence of atmospheric moisture, as described, for example, in FR-A-1,248,826 and FR-A-1,423,477.
However, these two patents neither describe nor suggest that the silicone composition can be in the form of an aqueous dispersion.
Furthermore, the prior art relating to aqueous silicone dispersions does not describe the use of aminosilane and/or amidosilanes in combination with an aqueous emulsion of an .alpha.,.omega.-(dihydroxy)diorganopolysiloxane and, optionally, a metal curing catalyst.